); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Hi Brian:
I used to use "Balco" (as far as I can remember) positive coefficient resistors that had specs similar to the Digikey units you linked to. These were only available in values under 200 Ohms and have a positive linear coefficient. The more common negative coefficient type like: <http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=207036> have a much larger change with temperature and so are a very common way to sense a set point. When a resistor with the same value is used to make a half bridge the voltage change around the balance point is nearly linear. There's a way to fit a third order polynomial to the data and once you have the coefficients it's only a linear equation to solve for converting resistance back to temperature. Have Fun, Brooke Clarke http://www.PRC68.com http://www.precisionclock.com http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Cam [EMAIL PROTECTED] wrote: > ); SAEximRunCond expanded to false > Errors-To: [EMAIL PROTECTED] RETRY > > Try DigiKey pn: 235-1123-ND for a simple PTC Thermistor that can be > soldered to the xtal case if one were so inclined. Do so at your own > risk to the xtal! > > -Brian > > > -------------- Original message ---------------------- > From: John Ackermann N8UR <[EMAIL PROTECTED]> > >>[EMAIL PROTECTED] said the following on 10/10/2007 02:17 PM: >> >>>In a message dated 10/10/2007 11:13:21 Pacific Daylight Time, [EMAIL >>>PROTECTED] >>>writes: >>> >>> >>>>We first built a small proportional heater circuit that we could shove >>>>in next to the crystal, and that worked OK. We finally found a source >>>>for thermistors spot welded to a spring clip that would mount snugly >>>>directly to the crystal case. With 12 volts applied, these heated the >>>>crystals very nicely. With the heaters, we were able to keep the >>>>systems running year round with about 1/10 the service calls. >>> >>>Hi John, >>> >>>interesting anecdote! >>> >>>Would you know if the thermistors are still available? Who made them? >> >>We bought them as a replacement part from Yaesu USA. This data is 10 >>years or more old, but here you go: >> >>Part Name Yaesu Part Number Murata Part Number >>Posistor G9090019 PTH507A01BG330N020 >> >>They used to be about $7.00 each. Yaesu's parts-order phone number at >>the time was (800) 255-9237. I'm not sure if there's another source for >>the Murata part; back then, we couldn't find one. >> >>Amazingly, I still have a web page documenting all that we learned about >>those cursed radios, including the schematic of our original homebrew >>heater design: http://www.febo.com/hamdocs/d4art.html. The quality of >>the heater schematic isn't very good, but it's all I have. >> >>John >> >>_______________________________________________ >>time-nuts mailing list -- [email protected] >>To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>and follow the instructions there. > > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
